Adopt Sorbet with Tapioca-generated RBIs

[dduugg]

Sets up static type checking with Sorbet and Tapioca, and raises every runtime file under lib/ to # typed: strict. Nothing changes at runtime. sorbet-runtime stays out of the gemspec. The # typed: sigils and the RBS comment signatures (#: (String) -> bool) are only comments, and nothing under lib/ references T. sorbet/ isn't part of spec.files.

This undoes the Sorbet: Enabled: false block from #76, which was there because the gem didn't use Sorbet.

Commits

1. Adopt Sorbet with Tapioca-generated RBIs (29 files, the hand-written part)
   • Gemfile: add sorbet and tapioca, plus railties so Sorbet can resolve Rails and ActionController in lib/singed/railtie.rb. Adding railties moves activesupport and activejob from 8.1.3.1 to 8.1.4.
   • sorbet/config (with --enable-experimental-rbs-comments), sorbet/tapioca/config.yml, bin/tapioca.
   • sorbet/tapioca/require.rb lists the gems and stdlib singed uses, plus sidekiq/api, sidekiq/testing and zeitwerk. The sidekiq and railties annotations and spec/support/sidekiq.rb refer to those.
   • # typed: sigils on every file under lib/ and spec/. spoom srb bump raised the files that type-check to typed: true, and commit 4 raises all of lib/ to strict. The spec files stay at typed: false, because Sorbet doesn't know the RSpec matchers.
   • .rubocop.yml: the Sorbet department is on again.
     • The files below typed: strict are listed in .rubocop_todo.yml under Sorbet/StrictSigil.
     • Sorbet/ConstantsFromStrings is disabled inline where the job class is looked up by the name in a Sidekiq payload. That lookup can only happen at runtime.
   • AGENTS.md: add the type-check and RBI regeneration commands.
2. Generate gem RBIs and annotations with Tapioca (77 files, about 302k lines). This is the unedited output of bin/tapioca gems --all and bin/tapioca annotations, marked linguist-generated.
3. List every RuboCop plugin in the Gemfile. rubocop-performance, rubocop-rake, rubocop-rspec and rubocop-sorbet were only in the bundle as dependencies of rubocop-gusto. They are now listed directly. The lockfile change is limited to DEPENDENCIES. .rubocop.yml also lists rubocop-sorbet in plugins now, instead of loading it only through rubocop-gusto's config.
4. Promote lib/ to typed: strict with RBS comment signatures (18 files)
   • Every method, attribute, and instance variable under lib/ has an RBS comment type. Casts use the comment forms (#: as !nil, #: self as Singed::Railtie, #: as untyped), so nothing needs sorbet-runtime. The style follows sidekiq-gusto.
   • Block-taking methods are generic, so flamegraph { 42 }, Flamegraph#record and the Sidekiq middleware's call return the block's type.
   • sorbet/rbi/shims/ covers what the generated RBIs miss:
     • the ActiveSupport::BacktraceCleaner and StackProf::Report ivars that singed reads;
     • StackProf::Report#frames;
     • a requires_ancestor on Sidekiq::Job.
   • A few method bodies change shape so Sorbet can narrow nilable values. Behavior is unchanged.
     • Singed.silence_line? and filter_line read backtrace_cleaner into a local.
     • CLI#run reads @filename directly.
     • Report#filter! reads @data into a local.
     • Flamegraph#record declares its block.
   • Singed.backtrace_cleaner is typed untyped, not ActiveSupport::BacktraceCleaner. Tapioca rewrites a gem's RBS comments into runtime sigs while it loads an app. In an app without ActiveSupport, that constant can't resolve, and the two methods would lose their sigs in the app's RBI.
   • ControllerExt::ClassMethods#flamegraph accepts a Symbol, a String, or an Array of them, like Rails' only:.
   • README: a controller that Sorbet checks needs an explicit include Singed::ControllerExt. The Railtie's include happens at runtime, so without it Sorbet checks flamegraph :show against Kernel#flamegraph, which is typed now.
   • .rubocop_todo.yml no longer excludes lib/ from Sorbet/StrictSigil, so RuboCop keeps lib/ strict.
   • AGENTS.md documents the conventions, including why these signatures still matter at runtime for apps that use Tapioca.
5. Run srb tc in CI. A Sorbet workflow, modeled on the RuboCop one, runs bundle exec srb tc on every push and pull request. Its Sorbet check is now a required status check on main.

Verification

• bundle exec srb tc: no errors
• bundle exec rspec: 42 examples, 0 failures
• bundle exec rubocop: no offenses
• bin/tapioca check-shims: no duplicates
• bin/tapioca gems --verify: all RBIs up to date
• Loading every file under lib/ without Bundler (so sorbet-runtime can't load), with and without Rails, Sidekiq and RSpec loaded: T stays undefined.
• The RBS comments in lib/singed.rb, translated to sigs the way Tapioca does it, evaluate without ActiveSupport loaded.

Not in this PR

• CI for bin/tapioca gems --verify. Until that exists, nothing stops the RBIs from going stale.
• Raising the spec files above typed: false.
• A pre-existing bug: with Singed.enabled = false, flamegraph { } raises NoMethodError from StackProf::Report#frames, because Flamegraph#save builds a report from a nil profile. The StackProf shim's @data type records this; the behavior is unchanged.